The subject matter of the present invention is a method for the modification of starch with organofunctional alkoxysilanes and alkylalkoxysilanes in the presence of organic solvents. The modified starch obtained by this method contains the organosilane in bound form and can be used directly for known applications.
It is known, for example, from U.S. Pat. No. 3,398,015 to produce self-supporting films from amylose, and to improve the properties of these films by treatment with alkyl chlorosilanes.
It is furthermore known to use starch as a filler in polymers, e.g., in urethane resins (see for example EP-A1 No. 0,058,921). Starch is known as a filler in other thermoplastics as well, such as polyolefins, for example, or also in elastomers (cf. Shell Polymers, Vol. 5, No. 3 (1981), pp. 73 to 78). Starch derivatives such as the ethers or esters, for example, are also used as fillers. It has also been proposed to use fillers made of starch derivatives containing silicones; in this case, however, the starch is merely mixed with the silicone, so that naught but a mixture of starch and silicone is involved, in which the silicone is not bound to the starch.
When starch is used as filler, it is to have both an oleophilic surface and reactive centers which improve its incorporation into the polymer and its adherence to the latter. For this purpose, organosilanes are used as adhesivizers between polymers and inorganic fillers, and in this case the fillers can also be modified fillers. The modification is performed by causing the fillers to react with the organosilane by putting the filler in contact with the organosilane directly or dissolved in a solvent. Additional reactivizers or catalysts are unnecessary in this reaction.
Now, if by analogy to this known modification to inorganic fillers for polymers, the attempt is made to modify starch with organofunctional alkoxysilanes and alkylalkoxysilanes which are dissolved in a solvent, the desired results are not obtained: The named alkoxysilanes dissolved in solvents react poorly or not at all with starch; modification of the starch does not occur, and the organosilane contained in the solvent merely adheres superficially to the starch.
Consequently, on the basis of the need perceived in practice of modifyibng starch with silanes, the problem existed of finding a method of fixing organofunctional alkoxysilanes and alkylalkoxysilanes out of solvents onto starch. The starch must then have reactive centers which, for example on the basis of the organofunctional radicals in the case of organofunctional alkoxysilanes, are able to react in a known manner with functional groups of polymers, or which cause the starch, on the basis, for example, of the alkyl radicals of alkoxysilanes, to become highly hydrophobic, resulting in good dispersibility and a uniform distribution of the starch in the polymer.